In the production of plants it is of importance to the well-being and the growth of the plants that the temperature and the humidity of the air are kept at a suitable level and that there is only a restricted temperature difference between the foliage and the root system. Thus, the root temperature of the plants should not exceed the temperature of the foliage by more than about 8.degree. C.
In greenhouses in the northern hemisphere, a sunny day during the winter period yields significant heat surplus during the day whereas a large heat demand is required during the night. The heat surplus during the day is usually vented and will thus be lost whereas heat must be supplied during the night. The entire greenhouse is then heated in order to develop suitable temperature conditions for the plants.
In plant production it is known to use plant trays having depressions ("pots") in which the seeds are sown or the plants are planted. At the bottom of these pots there are openings e.g. for drainage of surplus moisture upon watering. The plant trays may have a size of 30.times.40 cm and provide space for about 96 plants. The use of such plant trays suffers from the disadvantage that heat from the sun or other light sources may lead to undesirably high temperatures both in the plant stratum and in the roots with the consequence that the growth decreases. The plant trays are usually prepared from non-transparent plastics. Moreover, translucent plant trays would suffer from the same disadvantage because the support for the trays would then absorb surplus heat which would again be dissipated to the plants.
The foliage of the plants is also sensitive towards the rate of air flow to which it is exposed. This should not exceed about 0.4 m/sec.
In U.S. Pat. No. 3,492,761 an arrangement in a growth chamber is disclosed, the arrangement comprising a perforated floor for supporting plants thereon and serving to divide the growth chamber into an upper and a lower space. The floor is formed of sheet material shaped to include a series of parallel, spaced-apart ridges defining channels therebetween, the ridges extending substantially uniformly across the entire floor. The ridges have upper surfaces disposed sufficiently close together to support plant pots thereon with such pots straddling the channels. The channels have vertically extending sidewalls with holes extending therethrough for conditioned air to flow from the lower space in the growth chamber and generally horizontally into the channels in which the air dissipates kinetic energy and then at low velocity flows vertically upwardly from the channels into the upper space around the sides of the pots.
It is suggested in the U.S. patent specification that the floor may be constructed from sheet metal. Accordingly, by incident sunlight the floor will be very strongly heated with the risk of excessive heating of the plant roots, and the known arrangement does not offer the possibility of having climatically controlled air flowing around the root system of the plants at another velocity that the velocity of the air with which the foliage of the plants comes into contact, the conditioned air according to the known arrangement flowing upwardly at approximately the same velocity past the pot and the foliage of the plants.
It is an object of the invention to provide an arrangement in greenhouses or growth rooms enabling the heat consumption to be reduced and simultaneously ensuring that both plant roots and foliage are subjected to favourable climatic conditions and enabling uptake of surplus heat without subjecting the plants to inacceptable air movements, or enabling the surplus energy to be stored in a liquid filled tank or in another manner, thereby enabling energy savings and climatic control suitable for the production of plants both in conventional greenhouses and in growth rooms based on the supply of artificial light only.